Simon Kelner, the editor-in-chief of the Independent, described the online plagiarism row over star columnist Johann Hari as "politically motivated" and "fabricated anger" at lunchtime on Wednesday.

Speaking to Radio 4's The Media Show, Kelner said Hari's practice of not attributing some interviewees' quotes was wrong. But he sought to defend the award-winning columnist, saying it is not a great scandal and claiming that Hari had been unfairly vilified on Twitter.

Kelner confirmed that the paper is investigating which editors knew about Hari's interview technique and that they would review some of his past articles.

Writing in the Independent on Wednesday, Hari apologised for his practice of sometimes using quotes taken from other interviews and presenting them as his own.

"What Johann did was wrong. He accepts and we believe it," Kelner told The Media Show presenter Steve Hewlett.

"It was born from an honest ambition to give the clearest possible representation of what the interviewee was saying. In the grand scheme of things it is not a great scandal – it's a naive error which we recognise."

Kelner suggested Hari would not face any disciplinary action – other than being "spoken to at great length" – and said the young columnist had suffered punishment enough with the vilification he's had on Twitter.

He added: "Johann has been vilified by the Twittersphere for what he has done. I don't think you can discount [that an] element of it feels politically inspired [and] some of it is fabricated anger about what Johann has done."

Hari won the Orwell Prize for political journalism in 2008 for his work on American rightwingers, a report on Saudi Arabia, multiculturalism and women, and another on France's "secret war" in the Central African Republic.

A spokesman for the prize said on Wednesday that it was aware of the Johann Hari controversy and that it had a "process to follow in situations such as this and are doing so now".